Mystery of the swimming pool
With eyes above water, I can see the bottom of the pool very clearly, almost as if the water wasn't there. Refraction at the water level shifts the grout lines between tiles a little, waves make them dance, but the image of the bottom floor remains entirely sharp.
Once I dive just a few inches below the water level, I still can see the bottom, but it is sudenly entirely blurred as if viewed through the fog. Tiling in particular becomes unidentifiable.
Is this effect of biological, or physical nature?
I wear no goggles. The depth is four metres, the line of vision almost vertical. The water is warm, clean, comfortably low in chlorine. I have some reasons to expect water temperature distribution to be quite uniform on that particular day. I am hoping that this is easily reproducible in perhaps any deep enough public pool.
I am puzzled because I'd expect the optical conditions to degrade, and not improve, with additional distance and an additional medium in between.